The present invention relates to optical magnifying devices for magnifying a view of an object at a distance.
To magnify a view of an object or scene at a distance, the most common apparatus is a telescope. A well known telescope design is a Galileo telescope, which consists of a convex lens and a concave lens. The fundamental function of a telescope is to enlarge the angle of a light ray coming from the object at a distance. In a conventional telescope, a ray with an angle θ1 coming from an object whose distance is virtually at infinity is converted through the telescope into a ray with a larger angle θ2, where both angles are defined as angles with respect to the axis of the telescope. The eye sees the ray with angle θ2, and therefore, sees the object in the direction at angle θ2. Assuming θ2 is in proportion to θ1, the image of the object is magnified and the magnification is given by the ratio θ2/θ1.
More generally, any optical apparatus which converts the ray angle from θ1 to θ2 will magnify the view of the object at a distance. All such apparatus also converts the diameter of a collimated light beam from D1 to D2, where D2 is smaller than D1, and the magnification is given by the ratio D1/D2.
In a conventional telescope, the diameter of the collimated light beam emerging from the telescope determines the view area. Since the collimated light beam is compressed in diameter through the telescope, the view area is only a portion of the cross section of the telescope. To provide a sufficient view area, the diameter of the view area is usually 10 mm or larger. Therefore, conventional telescopes are at least a few centimeters long and cannot be built in a shape of a thin plate.
If the eye is distant from a telescope compared to the size of the view area of the telescope, the eye can view the image only within a small view angle. To view the image outside the view angle, an additional telescope may be placed beside the original telescope. Then the additional telescope provides the view in that direction. This concept may be extended to multiple telescopes, where each additional telescope provides the view in its direction. Several designs using multiple Galileo telescopes are disclosed in U.S. Pat. No. 5,270,859 and US patent application 20090128899. Combined with the multiple telescopes, the total range of the view area may be expanded, but the actual view is limited to the combined view areas of individual telescopes.
In the designs in the prior art using multiple Galileo telescopes, the dimension parallel to the light rays is several times greater than the telescope diameter. An important drawback in these devices is the aberration of the lens. In a conventional single Galileo telescope, the eye pupil is located within only a portion of the output light beam (given here as diameter D2). Actually, the size of eye pupil is much smaller than the beam size D2. Therefore, only a small portion of light in the beam diameter D2 is received by the eye. That is, a point on an object is viewed through only a small portion of each lens of the telescope and the image does not suffer much from the lens aberration. A different point on the object is viewed through a different portion of each lens. Since different points are viewed through different portions of each lens, the image could be distorted due to the lens aberration. However, the sharpness of the image is not equivalently degraded. In contrast to the conventional single Galileo telescope, the lens aberration in the multiple Galileo telescope directly affects the sharpness of the images, unless the beam diameter D2 is much larger than the eye pupil size. This is because all rays passing through the entire area of each lens produce a point in the image.
To reduce the length of the telescopes without sacrificing lens aberration, each telescope may be made with a small diameter, and then small D1. Then D2 will be further small. However, if the area of diameter D2, from which the light beam is emitted, is too small, the beam diverging effect due to diffraction impairs the sharpness of the image. Thus, reducing the telescope length is limited, and therefore, the multiple telescope designs of the prior art cannot be practically built on a scale of a thin plate.